Potentially tridentate ligands in the synthesis of methyl- and acetylpalladium(II) complexes

Article abstract of DOI:10.1002/1099-0682(200208)2002:8<2179::AID-EJIC2179>3.0.CO;2-3

The two protic tridentate ligands HNN′O (1) and HNN′S (2) were treated with [(COD)Pd(Me)Cl], and the corresponding methylpalladium(II) complexes [Pd(η²-HNN′)(Me)Cl] (1a and 2a) were isolated. The neutral ligands in these complexes coordinated the metal in an NN′ bidentate mode, through the pyridine and imine nitrogens, excluding the O or S atom from the coordination. This behavior was confirmed by X-ray diffraction analysis of the dichloro complex of 1, [Pd(η²-HNN′)Cl₂] (1c). Complexes 1a and 2a easily transformed quantitatively into the corresponding three-coordinate complexes [Pd(η³-NN′X)(Me)] (1b: X = O, 2b: X = S) in basic medium, with elimination of HCl. The complexes 1a and 1b were treated with PPh3 and P(CD3)3, respectively, resulting in 1e and 1h; 1a reacted further with a double quantity of PPh₃ to give rise to the diphosphane complex [trans-(PPh₃)₂Pd(Me)Cl] (1g) and free 1. The three-coordinate complexes 1b and 2b were subjected to CO bubbling at room temperature. In the case of 1b, acylation of the ligand on the phenolic oxygen was observed, with the formation of an organic acetate and release of palladium black. In the case of 2b, besides the acylated ligand on the thiohc sulfur, the acetylpalladium(II) complex [Pd(η³-NN′S)(MeCO)] (2c) was isolated. The X-ray structures of 1c·THF, 1b·1/2C₆H₆O₂, 2b, 2c·1/2CH₂Cl₂, and 1g have been solved. ( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).

Full text of DOI:10.1002/1099-0682(200208)2002:8<2179::AID-EJIC2179>3.0.CO;2-3

FULL PAPER
Potentially Tridentate Ligands in the Synthesis of Methyl- and
Acetylpalladium(II) Complexes
Alessia Bacchi,[a] Mauro Carcelli,[a] Corrado Pelizzi,[a] Giancarlo Pelizzi,[a] Paolo Pelagatti,*[a]
and Silvia Ugolotti[a]
Keywords: Carbonylation / Insertion / N ligands / Palladium / Tridentate ligands
The two protic tridentate ligands HNNЈO (1) and HNNЈS (2)
were treated with [(COD)Pd(Me)Cl], and the corresponding
methylpalladium(II) complexes [Pd(η2-HNNЈ)(Me)Cl] (1a
and 2a) were isolated. The neutral ligands in these com-
resulting in 1e and 1h; 1a reacted further with a double
quantity of PPh3 to give rise to the diphosphane complex
[trans-(PPh3)2Pd(Me)Cl] (1g) and free 1. The three-coordin-
ate complexes 1b and 2b were subjected to CO bubbling at
plexes coordinated the metal in an NNЈ bidentate mode, room temperature. In the case of 1b, acylation of the ligand
through the pyridine and imine nitrogens, excluding the O
or S atom from the coordination. This behavior was con-
on the phenolic oxygen was observed, with the formation of
an organic acetate and release of palladium black. In the
firmed by X-ray diffraction analysis of the dichloro complex case of 2b, besides the acylated ligand on the thiolic sulfur,
of 1, [Pd(η2-HNNЈ)Cl2] (1c). Complexes 1a and 2a easily
transformed quantitatively into the corresponding three-co-
ordinate complexes [Pd(η3-NNЈX)(Me)] (1b: X = O, 2b: X =
the acetylpalladium(II) complex [Pd(η3-NNЈS)(MeCO)] (2c)
was isolated. The X-ray structures of 1c·THF, 1b·1/2C6H6O2,
2b, 2c·1/2CH2Cl2, and 1g have been solved.
S) in basic medium, with elimination of HCl. The complexes ( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
1a and 1b were treated with PPh3 and P(CD3)3, respectively,
2002)
Introduction
pared the methylpalladium(II) complexes of the Schiff base
ligands
2-[(pyridin-2-ylmethylene)amino]phenol
(1,
HNNЈO) and 2-(1-pyridin-2-yl-ethylideneamino)benzene-
thiol (2, HNNЈS) (see b in Scheme 1). These chelating
agents are potentially tridentate and do not contain a hy-
drazone nitrogen. Compounds 1 and 2 were treated with
[(COD)Pd(Me)Cl], resulting in the isolation, under appro-
priate conditions, of two different kinds of methylpalla-
dium(II) complexes: [Pd(η2-HNNЈ)(Me)Cl] (1a and 2a) and
[Pd(η3-NNЈX)(Me)] (1b: X ϭ O, 2b: X ϭ S), which were
fully characterized. The reactivity of 1aϪb towards phos-
phanes and, in particular, the reactivity of the three-coord-
inate complexes 1b and 2b towards CO was investigated.
There is ongoing interest in the study of CO insertion
into PdϪC bonds, because of its importance as a key step
in many metal-catalyzed reactions.[1] Much work has been
done with both non-hybrid[2] and hybrid[3] bidentate li-
gands. In contrast, little has been done with tridentate li-
gands,[4] and there is a lack of data concerning the use of
protic tridentate ligands.[5] We have recently shown that the
use of protic tridentate HNNЈO acylhydrazonic ligands
(Scheme 1) resulted in the isolation of two different types of
methylpalladium(II) complexes: [Pd(η2-HNNЈ)(Me)Cl] and
[Pd(η3-NNЈO)(Me)].[6] These complexes showed different
reactivities towards CO: the first, in fact, gave rise to the
isolation of the corresponding acetyl complexes [Pd(η2-
HNNЈ)(MeCO)Cl] in excellent yields, whereas the second
resulted in the acetylation of the ligands on the hydrazonic
nitrogen, with concomitant formation of palladium black;
conversion was also quantitative in this case. The presence
of the basic hydrazone nitrogen was considered to be re-
sponsible for the instability of the complexes under CO at-
mosphere. With the aim of verifying this hypothesis, we pre-
[a]
Dipartimento di Chimica Generale ed Inorganica, Chimica
`
Analitica, Chimica Fisica, Universita degli Studi di Parma
Parco Area delle Scienze 17/A, 43100 Parma, Italy
Fax: (internat.) ϩ39-0521/905-557
E-mail: paolo.pelagatti@unipr.it
Scheme 1
Eur. J. Inorg. Chem. 2002, 2179Ϫ2187  WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ1948/02/0808Ϫ2179 $ 20.00ϩ.50/0
2179

A. Bacchi, M. Carcelli, C. Pelizzi, G. Pelizzi, P. Pelagatti, S. Ugolotti
FULL PAPER
corded in [D6]Me2SO shows a complicated pattern, which
prevents unambiguous assignment of the aromatic signals.
In the aliphatic region, however, three different species can
be distinguished: the expected complex 2a [singlets at δ ϭ
2.50 and 0.81 ppm, belonging to the C(Me)ϭN and
PdϪMe groups, respectively], and the products of solvent-
assisted ligand deprotonation [Pd(η3-NNЈO)(Me)] (2b, sing-
lets at δ ϭ 2.70 and 0.20 ppm) and [Pd(η3-NNЈO)Cl] (2d,
singlet at δ ϭ 2.84 ppm). As far as complex 2a is concerned,
it was not possible to establish the disposition of the methyl
and chloride ligands around the metal unequivocally, but
we assume that 1a and 2a have the same stereochemistry.
As a matter of fact, complex 1a is also not completely stable
in solution: in deuterated methanol or dimethyl sulfoxide it
slowly converts into the chloride complex [Pd(η3-NNЈO)Cl]
(1d) with elimination of methane (Scheme 2). This elimina-
tion is faster for 2a than for 1a, because 2 is more acidic
than 1. Interestingly, methane elimination also takes place
in the solid state, as confirmed by TGA analyses (1a:
158.3Ϫ198.1 °C, weight loss 6%; 2a, 103.3Ϫ149.0 °C,
weight loss 5%).
Results and Discussion
Synthesis of the Methyl Complexes 1a and 2a
The ligands HNNЈO (1) and HNNЈS (2) reacted with
[(COD)Pd(Me)Cl] in diethyl ether at room temperature to
afford the complexes [Pd(η2-HNNЈ)(Me)Cl] (1a and 2a in
Scheme 2). The reactions proceed with rapid displacement
of the labile diolefin COD by the incoming chelating pyrid-
ylimine ligands. These ligands coordinate to the metal in a
bidentate mode through the pyridine and imine nitrogen
atoms. The bidentate behavior of the ligand was confirmed
by the X-ray structure of the dichloro complex [Pd(η2-
HNNЈ)Cl2] (1c) (see crystallographic discussion). As previ-
ously reported for other methylpalladium(II) complexes
containing protic ligands,[6] diethyl ether is the solvent of
choice as the fast precipitation of 1a and 2a prevents meth-
ane elimination caused by ligand deprotonation, a process
that takes place easily in solution (vide infra). Complex 1a
is a yellow powder, while complex 2a is a gray powder. The
neutral character of the ligand was indicated by the IR
stretching bands of the OH and SH bonds, centered at 3377
cmϪ1 and 3229 cmϪ1, respectively. The structure of 1a pro-
1
Synthesis of the Methyl Complexes 1b and 2b
posed in Scheme 2 agrees with the H NMR spectrum: the
sequence of the pyridine protons is normal for pyridylimine
ligands in which both nitrogens are involved in coordina-
tion.[2b,6] A single isomer was detected, probably that with
the methyl ligand cis to the imino function. This is in fact
the preferred configuration for this type of complex.[2]
Moreover, the chemical shift of the methyl group is unusu-
ally low (δ ϭ 0.41 ppm in CDCl3 and δ ϭ 0.54 ppm in
MeOD, as compared to δ ϭ 0.8Ϫ1.1 ppm normally), prob-
ably because of the shielding effect of the neighboring aro-
matic ring.[7] The 1H NMR spectrum of complex 2a re-
When the reaction between 2 and (COD)Pd(Me)Cl was
carried out in THF in the presence of a slight excess of a
base, such as NaOMe or Et3N, elimination of HCl took
place and the reaction proceeded with a drastic color
change, from yellow to green. During the stirring the solu-
tion released the three-coordinate methyl complex [Pd(η3-
NNЈS)(Me)] (2b) as a green powder (Scheme 2). The an-
ionic character of the ligand was attested to by the disap-
1
pearance of the IR and H NMR signals of the SH group.
The methyl ligand resonates at δ ϭ 0.15 ppm, a value sim-
ilar to those found for other methylpalladium(II) complexes
in which the metal is bound to an anionic tridentate li-
gand.[6]
With 1, the corresponding process had to be carried out
in the presence of nBuLi instead of NaOMe or Et3N. In
this way, the deprotonation of the ligand was complete and
the reaction was able to proceed smoothly, with a drastic
color change from yellow to purple. The three-coordinate
methyl complex [Pd(η3-NNЈO)(Me)] (1b) precipitated from
the solution as a purple solid (Scheme 2). The same product
could be obtained by deprotonation of 1a by nBuLi or Na-
OMe in THF. The tridentate character of the ligand was
corroborated by the disappearance of the spectroscopic OH
signals; the methyl ligand is found at δ ϭ 0.60 ppm, a
higher value than found for 2a, but still shielded with regard
to the value usually found for methylpalladium(II) com-
plexes with bidentate nitrogen ligands.[2b,3,8] The trans influ-
ence of the methyl attached to palladium is well attested to
by the shielding undergone by the imine proton relative to
the free ligand: δ ϭ 7.88 ppm for 1b and δ ϭ 8.71 ppm
for 1.
Single-crystal diffraction analysis of 1b·1/2C6H6O2 and
2b confirmed the proposed structures (see crystallographic
discussion).
Scneme 2
2180
Eur. J. Inorg. Chem. 2002, 2179Ϫ2187

Methyl- and Acetylpalladium(II) Complexes
FULL PAPER
Reactions of 1a and 1b with Phosphanes
2-H [Scheme 1(b)].[2b,6] The methyl ligand now resonates at
δ ϭ 0.25 ppm (δ ϭ 0.60 ppm in 1b) as a singlet, while the
singlet of a coordinated phosphorus is now present in the
31P NMR spectrum at δ ϭ 41.3 ppm. In conclusion, the
phosphane replaces the pyridine ring in the coordination
In order to investigate the complexation strength of the
ligand 1, and before dealing with the carbonylation reac-
tions, the complexes 1a and 1b were treated with PPh3 and
P(CD3)3. When complex 1a was treated with a stoichi-
ometric amount of PPh3 in [D6]DMSO, an immediate color
change took place. The 31P NMR spectrum of the reactant
mixture showed a strong signal at δ ϭ 40.5 ppm, a value
characteristic for a phosphane coordinated to palladium,
and a second, much less intense, singlet at δ ϭ 32.5 ppm.
No signals belonging to free PPh3 were visible. The first
resonance was attributable to a species in which the ligand
was monodentate through a nitrogen atom and the square-
planar coordination was completed by the methyl ligand,
the chlorine atom, and PPh3 (1e in Scheme 3). The second
signal was tentatively attributed to the chloro(phosphane)-
palladium complex 1f (Scheme 3) , with the deprotonated
ligand coordinating palladium through the imine nitrogen
and the oxygen, and the square-planar coordination being
completed by a PPh3 molecule and a chlorine atom. Com-
plex 1f is formed by the reaction between PPh3 and 1d, the
formation of which has previously been described in Me2SO
solution. The addition of double quantities of PPh3 resulted
in the immediate precipitation of trans-[(PPh3)2Pd(Me)Cl]
and the consequent displacement of 1 (Scheme 3). The di-
phosphane complex is completely soluble in chlorinated
sphere,
giving
rise
to
the
complex
[Pd(η2-
NO){P(CD3)3}(Me)] (1h, Scheme 4). On the basis of literat-
ure spectroscopic data,[9] we assume that the methyl is trans
to the oxygen and the phosphane trans to the imine nitro-
gen (Scheme 4).
Scheme 4
Carbonylation Reactions
Dichloromethane solutions of 1b and 2b were subjected
to CO bubbling at room temperature. In both cases the
formation of palladium black was observed. As in the case
of the methyl complexes of NNЈO acylhydrazone ligands
studied previously,[6] the decomposition of 1b was very fast,
and after 5 min the solution was completely bleached. A
different behavior was observed in the case of 2b: after 3.5 h
of exposure to CO the solution was still light purple. After
removal of palladium, the resulting solutions were analyzed
by mass spectrometry: peaks relating to the acylated ligands
[m/z ϭ 240 (3) and 270 (4), respectively] were present in
both cases (Scheme 5). In the mass spectrum of the car-
bonylated solution of 1b, no signals belonging to the start-
ing complex or to an acetylpalladium complex were ob-
served, whereas the peak of the acetylpalladium complex
[Pd(η3-NNЈS)(MeCO)] (2c in Scheme 4, m/z ϭ 378) was
present in the corresponding mass spectrum of 2b. Such a
complex was isolated in a crystalline form by slow diffusion
of n-hexane into the refrigerated mother liquor; X-ray ana-
lysis confirmed the proposed structure (see crystallographic
discussion). Unfortunately, the few collected crystals did
not allow the spectroscopic characterization of the complex.
1
solvents, the H NMR spectrum recorded in CDCl3 show-
ing a triplet for the methyl ligand at δ ϭ Ϫ0.03 ppm with a
JP,H of 5.9 Hz, while in the 31P NMR spectrum the phos-
phanes generate a singlet centered at δ ϭ 27.7 ppm. The
structure of this complex was definitely established by X-
ray analysis. Crystals of trans-[(PPh3)2Pd(Me)Cl] were ob-
tained by slow diffusion of n-hexane into a refrigerated
dichloromethane solution. The methyl is trans to the chlor-
ide; coordination is planar within 0.08 A. Relevant coor-
dination features are: PdϪP1 ϭ 2.3272(5), PdϪP2 ϭ
2.3225(6), PdϪCl ϭ 2.4248(5), PdϪC ϭ 2.0574(4)A;
˚
˚
P1ϪPdϪP2
P1ϪPdϪC
ϭ
ϭ
177.49(2), P1ϪPdϪCl
91.69(1), P2ϪPdϪCl
ϭ
ϭ
88.85(1),
89.17(1),
P2ϪPdϪC ϭ 90.43(1), ClϪPdϪC ϭ 174.86(1)°.
Scheme 3
Scheme 5
The three-coordinate methyl complex 1b was treated with
a slight excess of P(CD3)3 in [D6]DMSO, and the reaction
was monitored by 1H and 31P NMR spectroscopy. After the
addition of the phosphane, the signals of an uncoordinated
The different reactivities shown by the two three-coordin-
pyridine ring appeared: in fact, the sequence of the hydro- ate methyl complexes are due in the case of 2b to the pres-
gen resonances, from low to high field, was 1-H, 4-H, 3-H, ence of a soft donor (the S atom), making the isolation of
Eur. J. Inorg. Chem. 2002, 2179Ϫ2187
2181

A. Bacchi, M. Carcelli, C. Pelizzi, G. Pelizzi, P. Pelagatti, S. Ugolotti
FULL PAPER
the acetyl complex 2c possible. This can definitely be viewed respectively) for tridentate NNЈX (X ϭ O, S) systems con-
as an intermediate in the acetylation of the ligand, as al- taining two five-membered chelated rings, as in the case of
ready proposed by other groups for methyl(alkoxo) and these complexes, than for NN-bidentate systems containing
methyl(thiolato)palladium(II) and nickel(II) complexes[10] only the PdϪN1ϪC5ϪC6ϪN2 chelation ring (Ͻ80° and
and by us for hydrazonic palladium(II) complexes.[6] On the Ͻ116°, respectively). The enlargement of the endocyclic
basis of the reactivity shown by 1b toward P(CD3)3 (see angles upon tridentate coordination correlates well with a
complex 1h), it is plausible to suppose that the CO coor- shortening of the PdϪN2 bond, ranging between 1.92 and
˚
˚
dination occurs with concomitant pyridine displacement. 1.98 A for tridentate complexes and 1.98 and 2.28 A for
The subsequent step could be the migration of the methyl bidentate complexes (with the exception of two NNN-tri-
onto the coordinated CO molecule, followed by coupling dentate compounds in which the third donor atom belongs
between the ligand and the acetyl group.
to a flexible six-membered chelation ring). The elongation
˚
of the PdϪN2 distance in 1b [2.009(3) A] compared to
II
˚
Structures of Complexes 1c·THF, 1b·1/2C6H6O2, 2b, and
2c·1/2CH2Cl2
those (1.917Ϫ1.944 A) observed in similar NNO Pd hal-
ogen complexes of phenyl 2-pyridyl ketone benzoylhydra-
zone[11] is consistent with the trans influence of the methyl
group, as also attested to by the NMR spectroscopic data.
Complex 1c (Figure 1) crystallizes as a 1:1 THF solvate.
The ligand is NNЈ-bidentate [bite angle N1ϪPdϪN2:
80.1(2)°], the metal square-planar coordination being com-
pleted by two chloride ligands. The OH group is not in-
volved in the coordination. The terminal phenyl ring is
˚
The PdϪO1 distance [2.037(2) A] is in agreement with those
found for the above hydrazone complexes (PdϪO:
˚
2.017Ϫ2.033 A). The growth of good quality crystals of 1b
was favored by co-crystallization with hydroxyquinone, pre-
sent in traces in the THF used for recrystallization. In the
crystal structure, the hydroxyquinone is positioned on a
crystallographic center of inversion and bridges two sym-
metry-related complex molecules through strong
nearly
perpendicular
to
the
chelation
plane
[PdϪNϪCϪC(OH): 72.2(8)°], due to the hindrance of the
chloride ligand in the coordination plane [Cl2···O1 3.446(5)
˚
A]. The coordination geometry can be summarized as fol-
lows: PdϪN2: 2.018(6) PdϪN1: 2.034(6), PdϪCl1:
˚
O2ϪH···O1 hydrogen bonds [O2···O1: 2.697(4) A,
˚
2.290(2), PdϪCl2: 2.300(2) A; N2ϪPdϪN1: 80.1(2),
OϪH···O: 176(3)°], as shown in Figure 3.
N2ϪPdϪCl1:
N2ϪPdϪCl2:
174.0(2),
94.8(2),
N1ϪPdϪCl1:
N1ϪPdϪCl2:
94.2(2),
173.4(2),
Cl1ϪPdϪCl2: 90.93(8)°.
Figure 2. Perspective view of molecule 1b·1/2C6H6O2; thermal el-
lipsoids are drawn at the 50% probability level
Figure 1. Perspective view of molecule 1c·THF; thermal ellipsoids
are drawn at the 50% probability level; the solvent has been omitted
The molecular structure of 2b is shown in Figure 4, while
the most relevant geometric features are listed in Table 1.
The coordination is square-planar, with the ligand behaving
The molecular structure of 1b, shown in Figure 2, fea- as NNЈS-tridentate, and the methyl trans to the iminic N2.
tures NNЈO-tridentate coordination for the ligand, with the The hindrance of the methyl substituent at C6 produces a
methyl group trans to the iminic nitrogen. The whole com- minor deviation from planarity involving a slight rotation
plex molecule is perfectly planar (maximum displacement of the benzenethiol group around the C8ϪN2 bond
˚
less than 0.08 A), and two pentaatomic chelation rings are [C6ϪN2ϪC8ϪC9: Ϫ8.0(5)°]. The overall planarity is con-
˚
formed upon coordination. Table 1 lists the main bonding served (maximum deviation 0.16 A). The presence of the
features for 1b. The bite angles involved in the chelation are soft and bulkier S donor in the ligand has the effect of
typical for tridentate chelation in these systems. A survey opening the SϪPdϪN2 angle relative to the analogous
of the crystal structures of molecules containing a pyrid- OϪPdϪN2 angle in 1b [88.21(6) and 82.7(1)° for 2b and
ineiminic
pentaatomic
N(py)ϪC(py)ϪC(iminic)Ϫ 1b, respectively], with a consequent slight weakening of the
˚
N(iminic)ϪPd chelation ring was performed on the Cam- PdϪN2 bond [2.069(2) for 2b and 2.009(3) A for 1b]. The
bridge Crystallographic Database (release of October 2001). trans effect of the S atom also results in a lengthening of
The N1ϪPdϪN2 and PdϪN2ϪC6 angles appear in the the PdϪN1 bond [2.060(2) in 2b and 2.033(3) A for 1b].
˚
ranges 77.2Ϫ82.3° and 108.6Ϫ119.2°, respectively, and, as The dimensions of the S atom also seem to induce a com-
a general trend, they tend to be wider (Ͼ80° and Ͼ117° pression of the PdϪN2ϪC6 angle [115.2(2)°] from the usual
2182
Eur. J. Inorg. Chem. 2002, 2179Ϫ2187

Methyl- and Acetylpalladium(II) Complexes
FULL PAPER
˚
Table 1. Selected bond lengths (A) and angles (°) for compounds 1b·1/2C6H6O2, 2b, and 2c·1/2CH2Cl2
1b·1/2C6H6O2
2b
2c·1/2CH2Cl2
(two molecules)
PdϪN1
PdϪN2
PdϪO1
PdϪC13
O1ϪC12
N1ϪC5
N2ϪC6
N2ϪC7
C5ϪC6
C7ϪC12
2.033(3)
2.009(3)
2.037(2)
2.061(4)
1.327(4)
1.350(5)
1.278(4)
1.410(4)
1.474(5)
1.418(5)
PdϪN1
PdϪN2
PdϪS
PdϪC14
SϪC13
N1ϪC5
N2ϪC6
N2ϪC8
C5ϪC6
C8ϪC13
2.060(2)
2.069(2)
2.2382(9)
2.045(3)
1.762(3)
1.365(3)
1.290(3)
1.436(3)
1.498(4)
1.402(4)
2.070(7)
2.088(7)
2.251(3)
1.91(1)
1.750(9)
1.37(1)
1.27(1)
1.41(1)
1.46(1)
1.36(1)
2.062(8)
2.062(8)
2.241(3)
1.936(9)
1.761(8)
1.36(1)
1.28(1)
1.41(1)
1.47(1)
1.40(1)
N2ϪPdϪN1
N2ϪPdϪO1
N1ϪPdϪO1
N2ϪPdϪC13
N1ϪPdϪC13
O1ϪPdϪC13
C12ϪO1ϪPd
C5ϪN1ϪPd
C6ϪN2ϪPd
C7ϪN2ϪPd
N1ϪC5ϪC6
N2ϪC6ϪC5
N2ϪC7ϪC12
O1ϪC12ϪC7
80.9(1)
82.7(1)
163.6(1)
177.3(1)
101.1(1)
95.3(1)
110.1(2)
111.8(2)
115.6(3)
112.4(2)
116.0(3)
115.7(3)
113.0(3)
121.7(3)
N2ϪPdϪN1
N2ϪPdϪS
N1ϪPdϪS
80.22(8)
88.21(6)
168.43(6)
178.3(1)
98.3(1)
78.7(3)
86.7(2)
163.7(3)
177.6(4)
100.2(4)
94.0(3)
79.1(3)
86.8(2)
165.5(2)
173.3(4)
100.5(4)
93.1(3)
N2ϪPdϪC14
N1ϪPdϪC14
SϪPdϪC14
C13ϪSϪPd
C5ϪN1ϪPd
C6ϪN2ϪPd
C8ϪN2ϪPd
N1ϪC5ϪC6
N2ϪC6ϪC5
N2ϪC8ϪC13
SϪC13ϪC8
93.2(1)
96.69(9)
112.6(2)
115.2(2)
116.0(2)
115.9(2)
115.9(2)
115.5(2)
123.6(2)
96.4(3)
97.9(4)
110.8(6)
114.4(6)
114.8(6)
117.5(9)
115.1(9)
117.5(9)
123.6(8)
111.0(6)
114.0(6)
116.1(6)
118.0(9)
114.5(9)
116.7(8)
122.3(8)
Figure 3. Molecular assembly through hydrogen bonds in the
cocrystallization of 1b with hydroxyquinone
value for tridentate complexes; this has also been observed
in some other cases of similar complexes [115.8° in chloro(-
pyridine-2-carbaldehyde thiosemicarbazone-N,NЈ,S)pallad-
ium(II),[12] and chloro(2-formylpyridine 3-hexamethylene
iminyl thiosemicarbazone-N,NЈ,S)palladium(II)[13]].
Figure 4. Perspective view of molecule 2b; thermal ellipsoids are
drawn at the 50% probability level
[C6ϪN2ϪC8ϪC9: 33(1) and C21ϪN4ϪC23ϪC24:
Compound 2c crystallizes with two independent molec- Ϫ30(1)°]. The metal coordination planes (N, N S, C, Pd)
ules in the asymmetric unit, one of which is shown in Fig- are also affected, with maximum deviations from planarity
˚
ure 5. A dichloromethane molecule is also present in the of 0.22 and 0.14 A, respectively, for the two molecules. The
asymmetric unit. The two complex molecules have similar bite geometry of the PdϪNϪCϪCϪS chelation ring is not
geometries, and their relevant bonding features are listed in influenced by this conformational modification, as can be
Table 1. The insertion of the CO into the PdϪCH3 bond of seen by comparison of the corresponding bond angles of 2b
2b produces a remarkable modification in the geometry of and 2c (Table 1), whereas angular strains are induced in the
the resulting acylated complex 2c, the resulting ligand struc- PdϪNϪCϪCϪN chelation ring, which in 2c are generally
ture being significantly distorted, with deviations from narrower than in 2b. In particular, the NϪPdϪN bite angle
˚
planarity as large as 0.75 A, due to a rotation of the ter- is reduced to values typical for bidentate systems [78.7(3)
minal benzenethiol group around the CϪN bond and 79.1(3)° for the two molecules of 2c]. The modification
Eur. J. Inorg. Chem. 2002, 2179Ϫ2187
2183

A. Bacchi, M. Carcelli, C. Pelizzi, G. Pelizzi, P. Pelagatti, S. Ugolotti
FULL PAPER
of the coordination geometry upon introduction of the reactivity of 1b toward trimethylphosphane, it seems likely
acetyl ligand may be due to a larger trans effect determining that the CO coordination proceeds by the breaking of the
the elongation of the PdϪN2 bond than in the methyl com- Pd-py bond. The possibility of making such a reaction cata-
˚
˚
plex [PdϪC: 2.090(7) and 2.097(7) A in 2c and 2.069(2) A lytic is under investigation in our laboratories.
in 2b], and also to steric reasons involving the orientation
of the acetyl group around the PdϪC bond. It has been
shown that acetyl groups coordinated to square-planar Pd
or Pt atoms tend to orient themselves perpendicularly to
Experimental Section
General: All reactions were performed under an atmosphere of ni-
trogen by standard Schlenk techniques. Solvents were dried prior
to use and stored under nitrogen. Elemental analyses (C, H, N, and
S) were performed with a Carlo Erba Mod. EA 1108 apparatus.
Infrared spectra were recorded with a Nicolet 5PCFT-IR spectro-
the coordination plane, with dihedral angles between the
acetyl and the coordination planes varying in the 68Ϫ90°
range, and PdϪC bonds falling between 1.947 and 2.001
[6]
˚
˚
A. In 2c, the PdϪC bonds [1.91(1) and 1.936(9) A] are
significantly shorter than average, and the acetyl groups are
closer to the coordination planes [dihedral angles of 51.4(4)
and 31.7(7)°], thus increasing the steric crowding in the av-
erage molecular plane. In both molecules the acetyl optim-
izes electrostatic interactions with 2 through an orientation
of the methyl towards the ligand sulfur atom and the oxy-
gen towards the pyridine C1ϪH [CH3(acyl)···S: 3.35(1) and
1
photometer in the 4000Ϫ400 cmϪ1 range, as KBr disks. H NMR
spectra were obtained on a Bruker 300 FT spectrometer with SiMe4
as internal standard at 25 °C, while 31P{1H} NMR spectra were
recorded on a Bruker CPX 200 FT with H3PO4 (85%) as external
standard at 25 °C. MS-CI spectra (methane) were recorded on a
Finnigan SSQ 710 spectrometer, collecting negative ions; the relat-
ive intensities are reported in brackets. The thermogravimetric ana-
˚
˚
lyses were carried out under nitrogen atmosphere on
a
3.15(1) A; O(acyl) ···C(py) ϭ3.19(1) and 3.11(1) A].
PerkinϪElmer Delta Series TGA7 apparatus, with a programmed
temperature increment of 5 °C/min. The ligands HNNЈO (1)[14] and
HNNЈS (2)[15] were synthesized by slightly modified literature pro-
cedures. The reagents used in the syntheses of the ligands — PPh3,
P(CD3)3 and nBuLi (1.6  solution in n-hexane) — were commer-
cial grade and were used without further purification.
[(COD)Pd(Me)Cl] was synthesized as reported in the literature.[4b]
[Pd(η2-HNNЈ)(Me)Cl] (1a): Compound 1 (0.050 g, 0.252 mmol)
was dissolved in 30 mL of diethyl ether and [(COD)Pd(Me)Cl]
(0.066 g, 0.250 mmol) was added. The immediate precipitation of
a yellow powder was observed. The mixture was stirred at room
temperature for 1 h and then filtered, and the solid was washed
repeatedly with diethyl ether and dried under vacuum. Yield:
1
0.083 g (94%). H NMR ([D6]Me2SO): δ ϭ 0.41 (s, 3 H, Pd-Me),
6.89 (t, 1 H, 7-H), 6.98 (d, 1 H, 8-H), 7.08 (d, 1 H, 5-H), 7.16 (t,
1 H, 6-H), 7.91 (t, 1 H, 2-H), 8.14 (d, 1 H, 4-H), 8.27 (t, 1 H, 3-
H), 8.82 (d, 1 H, 1-H), 8.88 [s, 1 H, C(H)ϭN], 9.84 (s, 1 H, OϪH)
Figure 5. Perspective view of one of the two independent molecules
in the crystal structure of 2c·1/2CH2Cl2; thermal ellipsoids are
drawn at the 50% probability level; the solvent has been omitted
ppm. IR: ν˜ ϭ 3377 m (OH), 1597 mϪ1589 m (CϭN) cmϪ1
.
C13H13ClN2OPd (355.1): calcd. C 43.97, H 3.69, N 7.89; found C
44.00, H 3.71, N 7.85.
[Pd(η2-HNNЈ)(Me)Cl] (2a): Complex 2 (0.050 g, 0.219 mmol) was
dissolved in 20 mL of diethyl ether and [(COD)Pd(Me)Cl] (0.058 g,
0.219 mmol) was added. The rapid formation of a gray powder was
observed, and this was filtered off after two hours of stirring at
room temperature. The filtered solid was washed repeatedly with
diethyl ether and then dried under vacuum. Yield: 0.060 g 71%. 1H
NMR ([D6]Me2SO): δ ϭ 0.81 (s, Pd-Me), 2.50 [s, C(Me)ϭN] ppm.
The other signals overlapped with the signals of 2b and 2d. IR: ν˜ ϭ
3229 m (SH), 1587 m (CϭN) cmϪ1. C14H15ClN2PdS (385.2): calcd.
C 43.65, H 3.92, N 7.27, S 8.32; found C 43.63, H 3.85, N 7.19,
S 8.17.
Conclusions
We have reported the preparation of methylpalladium(II)
complexes containing protic tridentate ligands of the
HNNЈO and HNNЈS types. These ligands can adopt two
different coordination modes around palladium: η2-HNNЈ
when neutral, η3-NNЈX (X ϭ O or S) when deprotonated.
The reactivity of the three-coordinate complexes towards
phosphanes and CO has been investigated. As far as car-
bonylation was concerned, in the absence of soft donors
(1b) it was not possible to isolate the corresponding acetyl
complex, and the reaction product was an organic molecule
derived from the acetylation of the ligand (3). In the pres-
ence of a soft donor (the sulfur atom in 2b), however, isola-
tion of the carbonylated complex was successful, although
the major product of the reaction was the thioacetate 4,
derived from acetylation of the ligand. The formation of
the organic derivatives was accompanied by the release of
[Pd(η3-NNЈO)(Me)] (1b). Method a: Complex
1
(0.050 g,
0.252 mmol) was dissolved in 10 mL of THF and
[(COD)Pd(Me)Cl] (0.067 g, 0.252 mmol) was added, resulting in a
yellow solution that was stirred at room temperature for 5 min.
nBuLi (0.016 g, 0.252 mmol, 158 µL) was then added, to produce
a purple solution that was stirred for 3 h, filtered, concentrated,
and then treated with an excess of n-hexane. A purple solid was
filtered off, washed with n-hexane, and then dried under vacuum.
palladium black. According to the results of a study on the Yield: 0.072 g (90%). On slow evaporation of a THF solution of 1b,
2184 Eur. J. Inorg. Chem. 2002, 2179Ϫ2187

Methyl- and Acetylpalladium(II) Complexes
FULL PAPER
1
crystals of 1b·1/2C6H6O2 suitable for X-ray analysis were collected. 0.035 g (92%). H NMR (CDCl3): δ ϭ Ϫ0.03 (t, JP-H ϭ 5.9 Hz, 3
H, PdϪMe), 7.71Ϫ7.38 (m, 30 H, Ph) ppm. 31P NMR (CDCl3):
Method b: Complex 1a (0.050 g, 0.141 mmol) was dissolved in
δ ϭ 27.7 (s) ppm. Crystals suitable for X-ray analysis were collected
10 mL of THF, and NaOMe (0.011 g, 0.211 mmol) or nBuLi
from
a
refrigerated THF/n-hexane mixture of trans-
(0.008 g, 0.141 mmol, 88 µL) was added; the purple solution was
stirred at room temperature for 2 h, then filtered and concentrated,
and the product was precipitated with n-hexane and worked up as
described above. Yield: 0.039 g (85%). 1H NMR ([D6]DMSO): δ ϭ
0.60 (s, 3 H, Pd-Me), 6.37 (t, 1 H, 6-H), 6.72 (d, 1 H, 8-H), 7.00
(m, 2 H, 5-HϪ7-H), 7.21 (t, 1 H, 2-H), 7.38 (d, 1 H, 4-H), 7.76 (t,
1 H, 3-H), 7.88 [s, 1 H, C(H)ϭN], 8.15 (d, 1 H, 1-H) ppm. IR: ν˜ ϭ
1600 s (CϭN) cmϪ1. MS: m/z (%) ϭ 317 (43) [1b]Ϫ, 301 (19) [1b
Ϫ Me]Ϫ, 198 (100) [1]Ϫ. C13H12N2OPd (318.7): calcd. C 49.00, H
3.79, N 8.79; found C 49.09, H 3.85, N 8.75.
[(PPh3)2Pd(Me)Cl]. C37H33ClP2Pd (681.5): calcd. C 65.21, H 4.88,
N 4.11; found C 65.20, H 4.85, N 4.10.
Treatment of 1b with P(CD3)3: P(CD3)3 (0.007 g, 0.112 mmol, 8.7
µL) was added to the complex solution by micropipette, without
observation either of color changes or of solid formation. 1h: 31P
NMR: δ ϭ 43.1 (s) ppm. 1H NMR: δ ϭ 0.25 (s, 3 H, Pd-Me), 6.13
(t, 1 H, 6-H), 6.46 (d, 1 H, 8-H), 6.75 (t, 1 H, 7-H), 7.08 (d, 1 H,
5-H), 7.31 (t, 1 H, 2-H), 7.81 (t, 1 H, 3-H), 8.02 (d, 1 H, 4-H), 8.57
(d, 1 H, 1-H), 9.70 [s, 1 H, C(H)ϭN] ppm.
[Pd(η3-NNЈS)(Me)] (2b): Complex 2 (0.100 g, 0.438 mmol) was dis-
solved in 30 mL of THF. [(COD)Pd(Me)Cl] (0.116 g, 0.438 mmol)
was then added, and the resulting yellow solution was stirred at
room temperature for 5 min. NaOMe (0.035 g, 0.656 mmol) or
Et3N (0.066 g, 0.656 mmol, 91 µL) was added, producing a deep
green solution that was stirred for 1.5 h and from which a green
solid was released. The solid was filtered off, washed with cold
methanol and diethyl ether, and then dried under vacuum. Yield:
0.115 g (75%). On slow evaporation of a THF solution of 2b, crys-
tals suitable for X-ray analysis were collected. 1H NMR
([D6]DMSO): δ ϭ 0.15 (s, 3 H, Pd-Me), 2.70 [s, 3 H, C(Me)ϭN],
6.78 (t, 1 H, 7-H), 6.91 (t, 1 H, 6-H), 7.15 (d, 1 H, 5-H), 7.23 (d,
1 H, 8-H), 7.66 (t, 1 H, 2-H), 8.01 (d, 1 H, 4-H), 8.13 (t, 1 H, 3-
H), 8.35 (d, 1 H, 1-H) ppm. IR: ν˜ ϭ 1595 m (CϭN) cmϪ1. MS:
m/z (%) ϭ 349 (100) [2b]Ϫ. C14H14N2PdS (348.7): calcd. C 48.21,
H 4.05, N 8.03, S 9.19; found C 48.25, H 4.10, N 8.05, S 9.14.
Carbonylations of 1b and 2b: The complex (0.050 g, 0.157 mmol for
1b and 0.144 mmol for 2b) was placed in a Schlenk tube and dis-
solved under nitrogen in 15 mL of dichloromethane. CO was
bubbled through a glass capillary until complete saturation of the
solution (at least 5 min), the vessel was closed, and the CO atmo-
sphere was maintained for the required time. The solution was fil-
tered through Celite in order to remove palladium black, and ana-
lyzed by mass spectrometry.
Carbonylation of 1b (3): The formation of palladium black was
practically instantaneous, as was the bleaching of the solution. The
CO was released after 10 min. MS: m/z (%) ϭ 241 (48) [3]Ϫ, 199
(32) [1]Ϫ.
Carbonylation of 2b (2c and 4): The formation of palladium black
was much slower then in the case of 1b. The CO was released after
2 h. MS: m/z (%) ϭ 378 (2) [2c]Ϫ, 270 (100) [4]Ϫ, 228 (37) [2]Ϫ. A
portion of the solution was dried and redissolved in the minimum
amount of dichloromethane, and n-hexane was slowly diffused into
it at Ϫ18 °C; crystals of 2c·1/2CH2Cl2 suitable for X-ray analysis
were collected.
[Pd(η2-HNNЈ)Cl2] (1c): 1 (0.076 g, 0.383 mmol) was dissolved in
30 mL of methanol, and a methanol solution (30 mL) of Li2PdCl4
(0.100 g, 0.383 mmol) was added. The mixture was stirred at room
temperature for 2 h, producing a brown solid, which was filtered
off, washed with methanol, and dried under vacuum. Yield: 0.111 g
(77%). On slow evaporation of a THF solution of 1c, crystals of
1c·THF suitable for X-ray analysis were collected. 1H NMR
([D6]DMSO): δ ϭ 6.83 (t, 1 H, 7-H), 6.92 (d, 1 H, 8-H), 7.19 (m,
2 H, 5-HϪ6-H), 7.95 (t, 1 H, 2-H), 8.20 (d, 1 H, 4-H), 8.39 (t, 1
H, 3-H), 8.72 [s, 1 H, C(H)ϭN], 9.06 (d, 1 H, 1-H), 10.01 (s, 1
Crystal Structure Determinations of 1b·1/2C6H6O2, 1c·THF, 2b,
2c·1/2CH2Cl2, and trans-[(PPh3)2Pd(Me)Cl]: Single crystals were
mounted on glass fibers, and X-ray diffraction data were collected
at room temperature on a BrukerϪSiemens SMART AXS 1000
equipped with a CCD detector for compounds 1b·1/2C6H6O2, 2b,
and 2c·1/2CH2Cl2, and a Philips PW1100 diffractometer equipped
H, OϪH) ppm. IR: ν˜ ϭ 3423 s (OϪH), w (CϭN) 1615 cmϪ1
.
with
a
scintillation
counter
for
compounds
trans-
C12H10Cl2N2OPd·THF (447.62): calcd. C 42.93, H 4.05, N 6.26;
found C 42.95, H 4.10, N 6.24.
[(PPh3)2Pd(Me)Cl] and 1c·THF. Graphite-monochromated Mo-Kα
˚
radiation (λ ϭ 0.71069 A) was used in all cases. Data collection
[Pd(η3-NNЈO)Cl] (1d): Characterization was performed only in so-
details for 1b, 2b, and 2c are: crystal to detector distance: 5.0 cm,
hemisphere mode, time per frame: 30 s, oscillation ∆ω ϭ 0.300°.
Data reduction was performed by use of the SAINT package[16]
and data were corrected for absorption effects by the SADABS[17]
procedure. For trans-[(PPh3)2Pd(Me)Cl] and 1c·THF, data were
processed with a peak-profile procedure and corrected for Lorentz,
polarization, and absorption effects (Ψ-scan method). Crystal de-
cay was negligible in all cases. The phase problem was solved by
direct methods[18] and the structures were refined by full-matrix,
least-squares on all F2,[19] by use of the WinGX package.[20] Aniso-
tropic displacement parameters were refined for all non-hydrogen
atoms, while hydrogen atoms were partly located from Fourier
maps and refined isotropically, and partly introduced at calculated
positions. Use was made of the Cambridge Crystallographic Data-
base[21] facilities for structure discussion. Final maps were fea-
tureless. Data collection and refinement results are summarized in
Table 2.
1
lution. H NMR ([D6]DMSO): δ ϭ 6.48 (m, 2 H, 7-HϪ8-H), 7.05
(t, 1 H, 6-H), 7.39 (d, 1 H, 5-H), 7.61 (t, 1 H, 2-H), 7.77 (d, 1 H,
4-H), 8.16 (t, 1 H, 3-H), 8.43 (d, 1 H, 1-H) ppm; the C(H)ϭN
signal was obscured.
Reactions of 1a and 1b with Phosphanes: The complex (0.020 g,
0.056 mmol for 1a and 0.063 mmol for 1b, respectively) was dis-
solved in 0.75 mL of [D6]DMSO in a 5-mm NMR tube. The de-
sired amount of phosphane was added quickly, with the progress
1
of the reaction being monitored by H or 31P NMR spectroscopy
at 25 °C.
Treatment of 1a with PPh3: PPh3 (stoichiometric, 0.015 g,
0.056 mmol) was added; the solution instantaneously turned from
yellow to green. 1e: 31P NMR: δ ϭ 40.5 (s) ppm. 1f: 31P NMR:
δ ϭ 32.5 (s) ppm; (excess of PPh3): Additional PPh3 (0.015 g) was
added, resulting in the immediate precipitation of a white solid
(trans-[(PPh3)2Pd(Me)Cl]), which was filtered off, washed with
Me2SO and diethyl ether, and then dried under vacuum. Yield:
CCDC-178202
(1b·1/2C6H6O2),
-178203
(2b),
-178204
(2c·1/2CH2Cl2), -178205 (1g), and -178206 (1c·THF) contain the
Eur. J. Inorg. Chem. 2002, 2179Ϫ2187
2185

A. Bacchi, M. Carcelli, C. Pelizzi, G. Pelizzi, P. Pelagatti, S. Ugolotti
Table 2. Crystal data and structure refinement for 1b·1/2C6H6O2, 2b, 2c·1/2CH2Cl2, 1g and 1c·THF
FULL PAPER
1b·1/2C6H6O2
2b
2c·1/2CH2Cl2
1g
1c·THF
Empirical formula
Molecular mass
Crystal system
C16H15N2O2Pd
373.70
Triclinic
¯
P1
C14H14N2PdS
348.73
Monoclinic
P21/c
C15.5H15N2ClOPdS
419.21
Monoclinic
P21/a
C37H33ClP2Pd
681.47
Monoclinic
P21/n
C16H18Cl2N2O2Pd
447.62
Monoclinic
P21/n
Space group
Unit cell dimensions
(A, °)
a ϭ 7.124(2) α ϭ 95.40(1)
b ϭ 9.301(2) β ϭ 95.43(1)
a ϭ 7.353(3)
b ϭ 18.063(5) β ϭ
107.45(1)
c ϭ 10.417(3)
1319.9(8)
4
a ϭ 20.188(5)
b ϭ 7.665(3) β ϭ
98.66(2)
c ϭ 20.209(5)
3091(2)
a ϭ 12.367(3)
b ϭ 23.433(5) β ϭ
111.93(2)
c ϭ 11.891(3)
3197(1)
a ϭ 10.576(4)
b ϭ 15.753(6) βϭ
103.49(2)
c ϭ 10.938(4)
1772(1)
˚
c ϭ 11.408(3) γ ϭ 104.26(1)
723.9(3)
2
1.714
1.287
3
˚
Volume (A )
Z
8
4
4
Dcalcd. (Mg/m3)
Absorption coefficient
1.755
1.546
1.801
1.508
1.416
0.789
1.678
1.358
(mmϪ1
)
F(000)
374
696
1672
1392
896
θ range (°)
1.81Ϫ28.22
4404
3068 [R(int) ϭ 0.0161]
2579
2.25Ϫ28.08
7770
2915 [0.0231]
2378
2.04Ϫ21.96
11579
3769 [0.0763]
1959
3.13Ϫ26.10
6620
6320 [0.0572]
1434
3Ϫ30
5376
5145 [0.3492]
2644
5145/0/209
Reflections collected
Independent reflections
Observed reflections
Data/restraints/
parameters
3068/2/239
2915/0/219
3769/0/392
6320/0/371
Goodness-of-fit
Final R indices
[I Ͼ 2σ(I)]
0.964
0.945
0.0258, 0.0582
0.810
0.0402, 0.0732
0.621
0.0536, 0.1283
0.888
0.0735, 0.1770
R1 ϭ 0.0316, wR2 ϭ 0.0751
R indices (all data)
∆F maximum/
minimum (e/A )
R1 ϭ 0.0408, wR2 ϭ 0.0790
0.482/-0.440
0.0361, 0.0625
0.528/-0.653
0.1038, 0.0882
0.537/Ϫ0.604
0.2031, 0.1565
1.164/-0.576
0.1380, 0.2037
2.440/-4.537
3
˚
H. Løken, H. Kooijman, A. L. Spek, K. Vrieze, G. van Koten,
Inorg. Chim. Acta 1996, 252, 141Ϫ155. [3d] L. Crociani, G. Ban-
supplementary crystallographic data for this paper. These data
can be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; Fax: (in-
ternat.) ϩ44Ϫ1223/336Ϫ033; E-mail: deposit@ccdc.cam.ac.uk].
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[3e]
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[4c]
R.
`
The C.I.M. (Centro Interfacolta di Misure ‘‘Giuseppe Casnati’’) is
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thanked for technical assistance.
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